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Kansas State University researchers studying a fungal disease capable of taking out an entire wheat crop are finding new evidence that the pathogen is even more feisty than they originally thought.

Barbara Valent, a university distinguished professor of plant pathology, said that the wheat blast fungus appears to be capable of storing genes for disease-causing proteins (called effectors) in “mini-chromosomes,” which are smaller chromosomes present in some strains.

In effect, the fungus is storing effectors for later use in attacking the plant.

“Effectors are small proteins,” Valent said. “They are basically the tools that the fungus uses to cut off the plant’s defenses and cause disease. There are hundreds of these that the fungus produces. But in some cases, plants recognize individual effectors and trigger resistance to block infection. The fungus then overcomes this resistance by getting rid of the offending effector gene.”

Sanzhen Liu, an associate professor of plant pathology, led the study, which also included assistant professor David Cook. Liu said the discovery that the fungus can re-arrange its genetic components between the seven main chromosomes and extra mini-chromosomes points to its ability to rapidly adapt to defeat resistance.

“Before we started this project, we knew that some effector genes could move around, but typically they would move to the ends of the (main) chromosomes,” Liu said. “It’s a surprise that they are carrying those fragments to mini-chromosomes. We’ve found that the mini-chromosome can serve as a reservoir for effector genes, and that the fungus employs some strategy through the mini-chromosome to gain the advantage.”

The finding creates new challenges for scientists to stay ahead of new and emerging strains of wheat blast fungus, which was first found in Brazil in 1985 and has since spread to other parts of South America and South Asia.

“We’ve known for a long time that the fungus was able to throw away genes that were causing it a problem, but after a while, wouldn’t you think that the fungus would just kill itself if it keeps throwing away this gene and that gene?” Valent said. “It doesn’t. In fact, it gets those genes back, and when they come back, they come to new places in the chromosome.”

Finding effective solutions, she added, is not yet clear.

“There is no simple solution to wheat blast disease,” said Valent, who has studied this disease for the last decade and the related rice blast disease for more than 40 years.

“We need to understand better the mechanism by which the fungus re-arranges these effector genes, so that we can learn more about how we can intervene. Maybe we can find genes that aren’t so easily deleted. How to move our studies to real control is difficult. At this point, I don’t know.”

The researchers noted that they have found “a few effector” genes that don’t seem to be part of the fungus’ devious work: “So those may be more stable targets for resistance,” Valent said.

Wheat blast thrives in warm, wet environments, such as those found in South America, where growers have struggled with the disease for more than two decades. In 2016, it was found across the ocean in Bangladesh, surprising farmers and researchers and causing additional concern about its ability to spread rapidly throughout the world.

“The first time the disease showed up in Bangladesh, it affected 15 percent of the country’s total wheat area, and farmers were burning fields to try to get rid of it,” Valent said. “That didn’t work and many farmers just stopped growing wheat there.”

Valent has published a website with information about research on the disease, which is conducted in the heavily-secured Biosecurity Research Institute on the north end of the Kansas State University campus in Manhattan.

“Our group discovered the only effective resistance gene that is protecting wheat in the field right now,” Valent said. “The strains from the early days weren’t very aggressive on wheat, but strains causing disease now are extremely aggressive. So, the fungus has been getting worse and worse, and there is potential in the future for it to get even more so.”

“We are screening in the BRI for more resistance, but the problem with this disease is we are not finding many useful resistance genes. We have a handful that we are following up on, but they are not frequent. It’s hard to control.”

K-State’s work on wheat blast is funded by the U.S. Department of Agriculture’s National Institute for Food and Agriculture. The technology used to build a high-quality genome map was funded by the National Science Foundation.

Hidden in the stubble of 2019’s wheat harvest, wheat curl mites are moving to find sprouting volunteer wheat seedlings to inhabit and continue the life cycle of wheat streak mosaic virus. The wheat streak mosaic virus (WSMV) instigated by these mites seriously affects the total yield of a wheat crop.

On average, WSMV causes $75 million in losses to Kansas wheat farmers every year. Wheat Streak Mosaic can cause a yield loss of more than 80 percent. WSMV isn’t treatable, but it is preventable. If we take preventative measures now, future yields will improve exponentially.

The virus is spread by the wheat curl mite, which feeds on wheat and other grasses. Wheat curl mites and the virus must have green host tissue to survive on throughout the summer after harvest. They most commonly reside on volunteer wheat that blew out the back of the combine or shattered grain from hail storms that happened before harvest. The mites on the fallen kernels move to the sprouting volunteer seedlings as new plants emerge in the summer.

Volunteer wheat is considered a “green bridge” because it allows the wheat curl mites and the virus to survive the summer.

Losses due to WSMV depend on variety, weather, percentage of infected plants and the time of infection. The first visible symptoms usually pop up in April on the edges of fields near volunteer wheat. Yellow streaking and mosaic patterns on young leaves and stunted tillers are some of the first signs. Symptoms worsen as the weather warms. Leaves on the infected plants turn yellow from the tip down, but usually the leaf veins remain green the longest. This gives the appearance of a striped yellow and green leaf, if the leaf is able to unfurl completely at all.

The best way to prevent the spread of the wheat streak mosaic virus is to remove volunteer wheat and other grassy weeds. Volunteer wheat must be completely dead and dry for two weeks before planting a new wheat crop. Volunteer wheat and other grassy weeds can be killed with herbicides or tillage.

A second management practice to limit the spread of the virus is to avoid early planting. Plant wheat after the “hessian fly free date” for your area. In some areas in western Kansas where there is no Hessian fly-free date, farmers should choose to wait until late September or October to plant their wheat. Planting after these dates will reduce the risk for the new wheat crop and reduce wheat curl mites from moving to new locations of wheat.

In addition, there are a few wheat varieties with moderate resistance to this devastating disease. Hard white wheats Joe and Clara CL, as well as hard red winter wheat Oakley CL have performed well in areas with wheat streak mosaic.

This resistance is not perfect and these plants may still be susceptible to triticum mosaic or high plains mosaic viruses. The resistance to wheat streak mosaic is less effective at temperatures above 75 degrees Fahrenheit. Therefore, planting these varieties early for grazing can place fields at risk for disease-related yield losses.

Undoubtedly, the best method to control WSMV is controlling the volunteer wheat.

Be a good steward, and a good neighbor, when making these management decisions, and you might just be rewarded with a boost in bushels on your next wheat crop.

Farmers across the state have access to many of the most cutting-edge wheat varieties ever bred. These varieties are all created with performance in mind, so how can producers gain that coveted yield bump when the dozens of varieties at their fingertips are all, by-and-large, on a fairly level playing field? According to Dr. Romulo Lollato, Wheat and Forage Extension Specialist at Kansas State University, the genetics of all the newest varieties have improved to the point where agronomic practices now have an even greater influence on yield than variety selection does.

“I think we are at the point where we have so many excellent varieties that we don’t have to be quite as picky. There are a lot of really good options, so we have to look at management, as well,” said Lollato. “That’s what the last 19 years of data that we have collected is telling us – that management practices are very, very important.”

According to this data, management accounts for 44-77% of yield variation. Because of this large yield gap, Lollato says, “It is time to manage wheat.”

To no one’s surprise, region and irrigation make the top of the list for yield producing management practices, but application of foliar fungicide and sowing date are also incredibly important for both irrigated and dryland farmers. The largest yield drag was dual-purpose wheat used for grazing.

Sowing dates can have a huge impact on final yields, but the optimal sowing date varies by region. Western Kansas farmers have an optimal date of October 1, north central’s optimal date is October 10 and south central’s is October 12. Planting after these optimal dates can mean substantial yield penalties. The South Central region loses about 1.1 bushels per day for around 20 days following October 12, but that loss increases to around 2.7 bushels per day after those initial 20. North Central Kansas consistently loses about 2.1 bushels per day, while the western region loses a whopping 3.5 bushels.

Lollato and his team have also found that seed treatments (like insecticides and fungicides) have a higher yield bump in good seasons, while foliar fungicides are beneficial in all seasons, but have more yield gain in those higher yielding seasons. Micronutrient applications have had a negligible bump during high performing years, while they have a monster gain of 9.7 bushels per acre during low performance years.

Lollato’s research has also focused on sulfur. Kansas has seen the removal of sulfur from the soil during wheat production exceeding the amount of atmospheric deposition since 2000, which he attributes as an effect of the Clean Air Act. This legislation has meant lower levels of air pollution, but less pollution means less sulfur coming in during rainfall. Sulfur application has a slight yield drag of -.6 bushels per acre during high performing years (like 2016 and 2017) but had a net gain of around 4.9 bushels per acre during drier years like 2018. He also advised that while sulfur and nitrogen deficiencies tend to have a similar yellowed appearance in plants, sulfur tends to express a brighter yellow discoloration in the upper plant canopy while nitrogen discolors the lower canopy.L

Although management practices are the most reliable source of yield gain, variety traits can have an effect. Stripe rust resistance was the trait with the highest yield gain, but there are others to keep an eye on depending on region and management practices. In the western region’s irrigated wheat, stripe rust, coleoptile length, straw strength and winterhardiness are the highest yielding traits. For dryland wheat, those traits are drought tolerance, coleoptile length, first hollow stem date and stripe rust.

In the central region, if you’re planning on applying fungicide, look for medium to late heading, drought tolerance, acid soil tolerance and medium to short height. With no fungicide application, those high yielding traits are stripe rust tolerance, leaf rust tolerance, fall grazing potential, early heading date and drought tolerance.

These projects were funded by the Kansas Wheat Commission and the Kansas Wheat Alliance. For more information on these research projects and others, please visit kansaswheat.org and kswheatalliance.org.

President Donald Trump’s recent comments on wheat exports to Japan have generated some negative press among one of his biggest groups of supporters.

The Hagstrom Report says when the president was speaking in Pennsylvania, one of the topics was the U.S. trade deficit with Japan. Trump said, “They send thousands, even millions of cars to us. We send them wheat. That’s not a good deal. And they don’t even want our wheat. They do it because they want us to at least feel that we’re okay.”

The National Association of Wheat Growers responded quickly via Twitter. “Mr. President, Japan is the number one market for U.S. wheat exports on average, where we hold just over 50 percent of the market. They don’t buy our wheat because ‘they want us to feel okay.’ They buy it because it’s the highest-quality wheat in the world. That’s not fake news.”

The negative reaction to Trump’s statement followed farmers venting about the administration’s policies when Ag Secretary Sonny Perdue appeared at Farmfest in Minnesota.

*Editor note* Ag Secretary Perdue will be at the Nebraska State Fair on Friday, August 23 for a town hall event at 11:30 in the Raising Nebraska Building.

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